EF Core 3.1 中的 Include / ThenInclude 如何转化为 Inner Join

Question

I am using EF Core 3.1. I want Include() and ThenInclude to Produce Inner join But They are producing LEFT join . I am using Code-First approach. Following are my Sample Model

public class Employee
    {
        [Key]
        public int Id { get; set; }

        public string Name { get; set; }

        public string Gender { get; set; }

        public string Img1 { get; set; }

        public virtual EmployeeDepartment EmployeeDepartment { get; set; }
    }

And
    public class EmployeeDepartment
    {       
        public int DeptID { get; set; }

        [ForeignKey("Employee")]
        [Required]
        public int Id { get; set; }

        public string DeptName { get; set; }

        public virtual Employee Employee { get; set; }
    }

Following is the linq Query

var result= context.Employees.Include(dept => dept.EmployeeDepartment).ToList();

Which produces below Sql query in O/P window

SELECT [dept].[Id], [dept].[Gender], [dept].[Img1], [dept].[Name], [dept.EmployeeDepartment].[Id], [dept.EmployeeDepartment].[DeptID], [dept.EmployeeDepartment].[DeptName]
FROM [Employees] AS [dept]
**LEFT JOIN** [EmployeeDepartment] AS [dept.EmployeeDepartment] ON [dept].[Id] = [dept.EmployeeDepartment].[Id]

I want inner join to be produced .Any Suggestions are welcome.

Answer 1

You could try reverting the order of the query(eg child -> parent):

var result= _context.EmployeeDepartments.Include(dept => dept.Employee).ToList();

However that adds additional mental overhead and may not be what you are looking for. If your relationship is required in your domain model I would suggest sticking with your query, it shouldn´t impact performance because left and inner join in this case will give the same result.

PS: For the EmployeeDepartment class you configured Id as both the primary key(by convention) and foreign key(with data annotation). The DeptID property is not being used(which I guess was intended to be the PK).